1. Field of the Invention
The invention is related to a strain gauge and, more particularly, to a fabric-based strain gauge.
2. Description of the Prior Art
Strain gauge, or named strainometer, of the prior art used to be a metal wire formed by a resistor with a constant resistance, such as 120 ohm, 350 ohm, or 1000 ohm. Furthermore, based on the principle that the proportion of the change of the length of the metal wire and the change of resistance of the metal wire is directly proportional, when an external force, such as a pulling force, pressure, tension, and other forces, acts on the metal wire and causes change in the length of the metal wire, the change of its resistance and the change of its length are directly proportional. Therefore, we can calculate the strength of the external force by measuring the change of its resistance.
Because of the simple principle and convenient usage, strain gauge has been widely applied in the prior art for the measurement of many physical vectors, such as the strain gauge element disclosed in U.S. Pat. No. 5,199,519; the strain gage disclosed in U.S. Pat. No. 4,920,806; the force measuring apparatus that contains a strain gauge disclosed in TW Pat. App. No. 094200558; and the torque wrench with a plurality of strain gauges disclosed in TW Pat. App. No. 094205393.
Generally, strain gauge is mounted to a solid structure, such as buildings, machines, tools, in a Wheatstone Bridge form to measure the strength of force received by the solid structure or its deformation. Because the strain gauge as described above is usually mounted to the solid structure through adhesion, it is hard to be mounted on a living body, such as human body or limbs of animals, to measure the movement of the living body.
In another aspect, with the gradual change in age structure, more and more old people need medical care, and a variety of physical function monitoring apparatus have became the focus of the medical equipment industry. Recently, a lot of such apparatus/systems have been developed to monitor physical functions, such as respiration, heartbeat, body motion, etc. For example, the wireless medical monitoring method and system is disclosed in TW Pat. No. 125438; the physical function monitoring apparatus combined with mobile phone is disclosed in TW Pat. No. 179015; and the apparatus and method for monitoring physical function is disclosed in TW Pat. App. No. 091110321.
However, most of the physical function monitoring apparatus/systems as disclosed in the references above have to perform monitoring at a fixed location, thus reducing mobility, and it may fail to perform monitoring because of user's carelessness. Additionally, some of the monitoring apparatus as described above can be worn on a user, so as to perform monitoring at anytime and anywhere; however, the weight and size of these apparatus may be a burden or may cause difficulty in the movements of the user.
In summary, there is a need for wearable physical function monitoring apparatus and further for comfortably wearable physical function monitoring apparatus, especially combining with the use of the strain gauge.